Most versions of my bio mention both the fact that I'm a professional harper, and (to tie it to my writing) that I feel music and language are inextricably linked. I still have a clear memory of the first time this truly struck me. I was at the Somerset Folk Harp Festival in a class taught by Beth Kolle. She pointed out a particular motif in the Scandinavian music we were learning. She told us the pattern of notes was common because it echoed an end-of-sentence inflection in the language. Comparable motifs also appear in music written by English speakers, across different origins.
When arranging music for the harp, even purely instrumental, conventions of speech and singing apply. The hands come off the harp to punctuate - analogy intended - phrases. When the music has lyrics, these pauses often come at a comma, conjunction or the end of a sentence. Music breathes, regardless of whether a voice is involved.
Outside of the pattern of sentences, words themselves have sound and melody. J.R.R. Tolkien said that the phrase "cellar door" was one of the most beautiful in the English language, quite divorced from its meaning. When choosing the right word to use in a sentence, often the choice between synonyms is a question of flow, reflecting intent in rhythm. Short, sharp staccato words convey a different impression than long, fluid syllables.
To an extent, lyrics are the ultimate meeting of music and language, and they work best when it is a wholehearted marriage. One of my favorite lyric lines is from the old classic Big Yellow Taxi - "Paved paradise and put up a parking lot." The alliterative plosives punch, brought out further by the quick patter of the notes.
Lyrics flow most naturally when they match the pattern of language, as discussed above. In some cases, deliberately setting up lyrics to contradict the pattern of language can create an interesting effect, sharpening the listener's focus.
(Or it's just confusing - it took me the longest time to parse the last verse of Carrie Underwood's Last Name because of the musical distance between "This ring that just appeared" and "out of nowhere" - I kept threading it together wrong in my head.)
Where lyrics fall down, at least for me, is when the music is slave to the lyrics, melody and rhythm warped to fit in the appropriate words. A lesser offense (to me!), but still unsatisfying, is where the musical pattern results in odd, awkward or vapid word choices.
But when the two meet, ah, there's romance in the air. The music reinforces the words; the words fill the music with second life. I don't - I can't - compose, but I appreciate experiencing the result.